Add a new internal flag, KVM_MEMSLOT_GMEM_ONLY, to the top half of
memslot->flags (which makes it strictly for KVM's internal use). This
flag tracks when a guest_memfd-backed memory slot supports host
userspace mmap operations, which implies that all memory, not just
private memory for CoCo VMs, is consumed through guest_memfd: "gmem
only".
This optimization avoids repeatedly checking the underlying guest_memfd
file for mmap support, which would otherwise require taking and
releasing a reference on the file for each check. By caching this
information directly in the memslot, we reduce overhead and simplify the
logic involved in handling guest_memfd-backed pages for host mappings.
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
Reviewed-by: Shivank Garg <shivankg@xxxxxxx>
Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
---
include/linux/kvm_host.h | 11 ++++++++++-
virt/kvm/guest_memfd.c | 2 ++
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 26bad600f9fa..8b47891adca1 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -54,7 +54,8 @@
* used in kvm, other bits are visible for userspace which are defined in
* include/uapi/linux/kvm.h.
*/
-#define KVM_MEMSLOT_INVALID (1UL << 16)
+#define KVM_MEMSLOT_INVALID (1UL << 16)
+#define KVM_MEMSLOT_GMEM_ONLY (1UL << 17)
/*
* Bit 63 of the memslot generation number is an "update in-progress flag",
@@ -2490,6 +2491,14 @@ static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
vcpu->run->memory_fault.flags |= KVM_MEMORY_EXIT_FLAG_PRIVATE;
}
+static inline bool kvm_memslot_is_gmem_only(const struct kvm_memory_slot *slot)
+{
+ if (!IS_ENABLED(CONFIG_KVM_GUEST_MEMFD))
+ return false;
+
+ return slot->flags & KVM_MEMSLOT_GMEM_ONLY;
+}
+
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn)
{
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 67e7cd7210ef..d5b445548af4 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -578,6 +578,8 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
*/
WRITE_ONCE(slot->gmem.file, file);
slot->gmem.pgoff = start;
+ if (kvm_gmem_supports_mmap(inode))
+ slot->flags |= KVM_MEMSLOT_GMEM_ONLY;
xa_store_range(&gmem->bindings, start, end - 1, slot, GFP_KERNEL);
filemap_invalidate_unlock(inode->i_mapping);
--
2.50.1.470.g6ba607880d-goog
